Batteries (e.g. rechargeable Lithium-Ion batteries) are used extensively in electronic devices (e.g. notebook computers, cell phones and other portable electronic equipment). Rechargeable Lithium-Ion batteries are presently preferred primarily because of their relatively low cost and high-energy storage capability.
The increasing pressure to package more power into a given size battery cell seems to be approaching a technology limit for some particular cylindrical cell geometry, as evidenced by an increase in safety incidents where the cell has exploded, ruptured, or vented (a forced expulsion of gases). The safety hazards from such incidents, although rare, include the potential for causing a fire and the risk of burns and other injury from projectiles and ejected cell contents. This problem has exposed some battery vendors and equipment manufacturers to unacceptable liability risks, as evidenced in a number of well-publicized recalls.
All cells currently have an internal positive temperature coefficient current limiting device (PTC). The primary role of this PTC is to limit short circuit current on individual cells. It also serves a second level of protection by acting as the CID. These devices protect the cell from excessive internal pressure. If the pressure increases beyond a set limit, the CID should break and electrically disconnect the cell. Thus, the CID is configured to open the electrical path if an excessively high charge voltage raises the internal cell pressure beyond a predetermined level (e.g. to 10 Bar (150 psi)). The safety vent allows a controlled release of gas in the event of a rapid increase in cell pressure. Unfortunately, conventional CID arrangements have proven faulty, not breaking the electrical circuit during abnormal pressure and temperature events because of an incomplete disconnect.
Accordingly, a need has arisen for more reliable safety features for batteries that address the shortcomings of the conventional arrangements discussed above.